The invention relates to a shaped part for forming a guide ring for a gas turbine. It also relates to a gas turbine having a guide ring which is assembled from a number of shaped parts of this type.
Gas turbines are used in numerous sectors to drive generators or working machines. The energy content of a fuel is used to generate a rotary movement of a turbine shaft. For this purpose, the fuel is burnt in a combustion chamber, with air which has been compressed which has been compressed by air compressor being supplied. The working medium which is generated in the combustion chamber through the combustion of the fuel and is under a high pressure and at a high temperature is, in the process, guided via a turbine unit connected downstream of the combustion chamber, where it is expanded in a work-performing manner.
To generate the rotary movement of the turbine shaft, a number of rotor blades, which are usually combined in groups or rows of blades and drive the turbine shaft via a pulsed transfer from the flow medium, are arranged on the turbine shaft. Moreover, to guide the flow medium in the turbine unit, there are usually rows of guide vanes connected to the turbine housing between adjacent rows of rotor blades. To suitably guide the working medium, the guide vanes have a vane part, on the end side of which a blade root, which is also known as a platform, is formed integrally in order to secure the turbine vane to the respective supporting body. This platform, which is usually secured or hooked to an inner wall of the turbine unit, also, by means of its surface facing the interior of the turbine unit, delimits the flow region for the working medium flowing through the turbine unit. In order to form a flow passage with a relatively smooth internal surface for the working medium, the turbine unit usually additionally includes what are known as guide rings arranged between the platform of adjacent rows of guide vanes, as seen in the direction of flow of the working medium, which guide rings bridge the gap which is left by the platforms of adjacent guide vanes, as seen in the direction of flow of the working medium.
When designing gas turbines, in addition to the output which can be achieved, a particularly high efficiency is usually a design aim. For thermodynamic reasons, the efficiency can in principle be increased by increasing the outlet temperature at which the working medium flows out of the combustion chamber and into the turbine unit. Therefore, temperatures of approximately 1200xc2x0 C. to 1300xc2x0 C. are desired and indeed achieved for gas turbines of this type.
At such high temperatures of the working medium, however, the components and parts which are exposed to this medium are subject to high thermal loads. In order, nevertheless, to combine high levels of reliability with a relatively long service life of the relevant component, it is customary to cool the components in question. Accordingly, the guide rings arranged at the hot-gas passage are usually designed so that they can be cooled. In operation, they are heated relatively strongly, and consequently relatively high thermal expansion needs to be taken into account.
Cooling air is generally used as coolant in a gas turbine of this type, in the manner of an open cooling arrangement. The cooling air provided as coolant is in this case fed to the corresponding turbine blade or vane or component via an integrated coolant passage. Starting from this passage, the cooling air flows through the corresponding part in passages which branch off and are usually left open at the outlet end. After it has flowed through the respective component, therefore, the cooling air emerges from the component and, in so doing, is mixed with the working medium carried in the turbine unit.
However, the cooling action which can be achieved when cooling air is used as coolant is limited. Accordingly, for a gas turbine which is cooled in this way, the efficiency achieved is limited even when thermal barrier coatings are used for the thermally loaded components, especially since an increased demand for cooling would lead to losses in the compressor mass flow rate available for combustion, and these losses for their part can only be accepted to a limited extent. It may therefore be desirable to turn away from a cooling arrangement which is based on cooling air and to provide a cooling arrangement which uses cooling steam as cooling medium. However, in this case in particular the provision of a guide ring which can be cooled reliably and sufficiently, despite inherently being a relatively simple component, have proven particularly complex.
The invention is therefore based on the object of describing a shaped part for forming a guide ring for a gas turbine which can be produced with particularly little outlay and, moreover, can be cooled particularly effectively with steam as coolant. Moreover, it is intended to provide a gas turbine having a guide ring which can be cooled reliably with steam as cooling medium and can be produced particularly easily.
With regard to the shaped part, this object is achieved, according to the invention, by a base plate which, together with an associated metal guide plate, forms a flow passage for a coolant which, in cross section, extends over substantially its entire width, with respect to the axial direction of the guide ring.
The invention is based on the consideration that, to achieve a particularly simple and therefore also inexpensive design of the guide ring, the flow path for the cooling medium flowing through it should be kept particularly simple. To ensure particularly reliable cooling, there is provision for the piece of material which is exposed to the hot-gas side, namely the base plate, to be acted on over substantially its entire area. In order, in the process, to ensure that the flow path for the coolant is separated from the interior of the gas turbine, which is necessary when using steam as coolant, the base plate is assigned a metal guide plate in order to form a substantially closed, large-area flow passage.
Reliable cooling with relatively little outlay on cooling medium is made possible as a result of the metal plates and, in particular, the metal guide plate preferably being designed as a relatively thin metal plate.
When steam is being used as cooling medium, the flow path of the cooling medium should be particularly well separated from the flow space of the working medium in the turbine. In order, under this condition, to additionally allow steam, as cooling medium, to act on the base plate over substantially its entire area, with particularly simple means, it is advantageous for a second metal guide plate, which together with the first metal guide plate forms a flow-inlet space for the coolant, to be arranged on that side of the metal guide plate which is remote from the base plate. In this case, the flow-inlet space is expediently in communication, in an inflow region, with the flow passage formed by the first metal guide plate and the base plate. In this case, it is advantageous for a steam feedline to open out into the flow-inlet space.
In a further advantageous configuration, the shaped part is designed in a similar way in order to discharge the steam provided as coolant. In this case, a third metal guide plate is assigned to the second metal guide plate on its side which is remote from the first metal guide plate. This third metal guide plate, together with the second metal guide plate, forms a flow-outlet space for the coolant. The metal guide plates are expediently designed in such a manner than the flow-outlet space for the coolant is in communication, in a discharge region, with the flow passage formed by the base plate and the first metal guide plate. In this case, a steam discharge line advantageously opens out into the flow-outlet space.
Therefore, in addition to a base plate, a shaped part which is developed in this manner has at least three metal guide plates arranged one above the other in the manner of a stack. The intermediate spaces which are formed by in each case two metal guide plates or by one metal guide plate and the base plate are used, with specific objects, as flow space for the coolant, with a flow-inlet space, a flow passage and a flow-outlet space being provided. This results, in a particularly simple manner, in the creation of a shaped part which is complete in terms of its functionality and is particularly flexible. The use of metal guide plates makes it particularly simple to create the various flow regions for the coolant.
The outlay for cooling the shaped part is kept particularly low, since the metal guide plates used and/or the base plate used are kept particularly thin. In order, when using relatively thin metal plates, to ensure a particularly high mechanical strength and load-bearing capacity of the shaped part, the base plate, in a particularly advantageous configuration, has, on the top side, a number of reinforcing ribs which run substantially in the axial direction of the guide ring. They form flow passages for the coolant which are connected substantially in parallel.
The use of steam as coolant for the gas turbine requires a relatively high leak tightness of the corresponding steam feeds and discharges, so that leakage of the cooling steam into the flow region of the gas turbine is reliably avoided. In particular, the introduction of steam into and the discharge of steam from the guide ring should be particularly reliably sealed. For this purpose, it is possible to provide appropriate threaded pipe connections at the steam inlet and outlet of the shaped part. To create the space required for this purpose and, in particular, for fitting the corresponding steam lines, each shaped part which is provided for forming the guide ring is expediently designed to hook centrally into the gas turbine, as seen in the radial and axial direction of the guide ring. This is because a centrally configured hook connection of this type in particular makes it possible to maintain the feeds and discharges of coolant which are present in an open-cooled gas turbine in substantially unchanged form, while, when using steam as coolant, screw connections which have been modified only in the region of contact with the guide ring are used. In other words: with a design of this type, the space required to produce the coolant-side connections is provided by the central positioning of the hooked connection, without it being necessary to change the spatial arrangement or guidance of the coolant passages which are provided in an open-cooled gas turbine. Therefore, the design of an open-cooled gas turbine can be transferred to a closed-cooled gas turbine (with steam as coolant) using particularly little outlay in the style of xe2x80x9cDelta Engineeringxe2x80x9d.
A centrally arranged hooked connection of this type can be produced particularly easily, since a carrier hook is advantageously arranged on in each case a plurality of adjacent reinforcing ribs of the base plate, so as to form through-flow openings which are delimited by the base plate, in each case two adjacent reinforcing ribs and the respective carrier hook. The carrier hooks are therefore fitted individually onto in each case a plurality of, for example two to four, reinforcing ribs, with in each case a number of passages or through-flow openings for the coolant being formed below each carrier hook. Therefore, the coolant flows beneath the carrier hooks, so that particularly effective cooling becomes possible and, moreover, thermal stresses are kept at particularly low levels. In a further advantageous configuration, the or each carrier hook is arranged centered, as seen in the axial direction of the guide ring.
With regard to a gas turbine having a number of rotor blades, which have in each case been combined to form rows of rotor blades and are arranged on a turbine shaft, and having a number of guide vanes, which are in each case combined to form rows of guide vanes and are connected to a turbine housing, said object is achieved by the fact that a guide ring, which is assembled from a number of said shaped parts, is arranged in the inner region of the turbine housing.
In this case, the guide ring is advantageously arranged between the first row of guide vanes and the second row of guide vanes, as seen in the direction of flow of the working medium.
The advantages which are achieved by the invention consist, in particularly, in the fact that the metal guide plate assigned to the base plate allows the formation of a flow passage which, in cross section, extends substantially over the entire base plate, so that it is ensured that the base plate is exposed to coolant over substantially its entire area. The first metal guide plate and, in particular, also the second and third metal guide plates which are additionally provided lead, in a particularly simple manner and with particularly low production costs, in favorable guidance of the coolant in the region of the guide ring, the first metal guide plate being used to guide the coolant over the base plate which is exposed to hot gases while ensuring a desired cross section. The middle or second metal guide plate, by contrast, is used to provide guidance between this metal plate and the first metal guide plate, to an inflow region, from which the coolant passes into the flow passage formed by the base plate and the first metal guide plate. By contrast, the third metal guide plate, together with the second metal guide plate, forms a flow-outlet region for the coolant. A design of this type, which forms a set of metal guide plates, can be produced particularly easily, while also satisfying relatively high demands in terms of the leak-tightness.